Sanaria has pioneered the manufacture of aseptic, purified, cryopreserved I sporozoites (PfSPZ) suitable for controlled infection and immunization of humans. Human studies to date have demonstrated the potency of attenuated PfSPZ (PfSPZ Vaccine) for inducing protective immune responses and the infectivity of non-attenuated PfSPZ (PfSPZ Challenge) when administered intravenously to humans. Further development will focus on optimization of regimens that use PfSPZ to induce durable immunity against multiple strains of P. falciparum. The trials proposed here by Sanaria and LMIV will assess immunization with PfSPZ Challenge in individuals who receive antimalarial treatments that eliminate parasites during their liver stage of development, as a potential strategy for immunization called PfSPZ-CVac (chemoprophylaxis vaccine) to reduce the PfSPZ dose required for protective immunity, and to maximize activity against heterologous parasites. The design of the proposed clinical trial will entail 2 phases: 1) the pilot trial phase will determine the optimal timing after PfSPZ inoculation to administer the drug pyrimethamine that is approved by FDA for prophylaxis and treatment of susceptible P. falciparum malaria; 2) the main trial phase will assess the degree of protection against homologous parasites induced by immunization with PfSPZ and pyrimethamine treatment. During Year 1, the study team will complete all manufacturing, quality control release and stability assays, and regulatory requirements for successful submission of Investigational New Drug Application (IND) to the FDA and submit the IND for this new product, which combines elements that have already tested in humans (PfSPZ) or approved for human use (chloroquine, pyrimethamine); in the first year, we will also initiate screening and enrollment of study participants. During Year 2, we will conduct the pilot phase trial to finalize the optimal regimen, submit the main trial for IRB review, and initiate the main trial, and during Year 3 we will conduct the main trial controlled human malaria infection to demonstrate efficacy against homologous parasites. These trials will establish a new modality for immunization with PfSPZ, which can subsequently be assessed for protection against heterologous and naturally occurring P. falciparum infections.